Tiles cracked

[rabbit]

Our house has a sous-sol that is the same area as the ground floor. I noticed a fine crack in the 50cm ceramic floor tiles that extends across two tiles. The sub floor is concrete beams with concrete block infills.
I have looked at the ceiling of the sous sol where the problem is located. I can’t see any cracks or deformation but some of the concrete is covered with artex. House was built 17 years ago by a reputable local builder. The crack is so fine as to not pose any cosmetic issue at present.
What should I do?

[basquesteve]

Try and find replacement tiles and replace with a flexible adhesive something is moving